Retrodirective antenna array



July 23, 1968 w. J. wElss RETRODIRECTIVE ANTENNA ARRAY Filed Aug. 11, 1961 3,394,374 RETRODIRECTIVE ANTENNA ARRAY William J. Weiss, Los Angeles, Calif., assignor to Packard- Bell Electronics Corporation, Los Angeles, Calif., a corporation of California Filed Aug. 11, 1961, Ser. No'. 130,791 11 Claims. (Cl. 343-100) The present invention relates to directional antenna means for electromagnetic energy radiations and more particularly to antenna means for receiving electromagnetic radiations andautomatically directing the sensitivity pattern thereof toward the source of said -radiations Awhereby electromagnetic radiations may be transmitted back toward said source.

At the present time, it is frequently desirable to maintain communications between two remotely located stations by means of mobile installation where the amount of power available for operating radio receiving and/or transmitting equipment may be severely limited. Accordingly, it is very ydesirable to obtain an eticient transmission of the signals. One means of accomplishing this is to employ high gain antenna means having a sensitivity pattern which comprises a very narrow bea-m wid-th. When the antenna pattern is very narrow, the antenna must be properly oriented with respect to the-two stations. Unfortunately, when at least one of the stations is of a mobile nature, the bearing between the two stations may be constantly varying throughout a wide angle. As a result, it is necessary under such circumstances to employ some form of scanning of the antenna pattern. Although there are a large number o f means for mechanically and electronically scanning lan antenna array, it has been very difficult, if not impossible, to maintain the antenna pattern exactly oriented withrrespect to the two stations. As a result of these inaccuracies .in the aligning of the various antenna patterns, it has been customary to employ antenna patterns having a beam width that is somewhat wider than necessary. As a result of the excessive beam width, a certain amount of misalignment of the beam may be permitted. However, because of the wide beam width, the antenna does not provide the maximum sensitivity which might otherwise be obtained. This in turn fails to optimize the efficiency of the transmissions and has necessitated excessive amounts of power and/ or produced reception having low signal-to-noise ratios. 4

It is now proposed to provide antenna means that will overcome the foregoing difficulties. More particularly, .it is proposed to provide an antenna array and means for controlling the same thatwill automatically keep the pattern of the antenna centered on the axisof any signals being received so as to insure a maximum sensitivity of the receiving means. In addition, the antenna means may be reciprocal so that if it is desired, a return signal may be transmitted therethrough. Since the pattern of the antenna means will be automatically aligned with the direction of the received signal even though a very narrow beam width is employed for transmitting, it will always be properly oriented with respect to the other station.

More particularly, this is to be accomplished by providing antenna means and control means therefor which are adapted to receive electromagnetic radiations from any source located within a wide scan angle. The antenna means includes at least two elements that are spaced from each other and positioned to produce separate'signals that are proportional to the electromagnetic energies incident thereon. Since these elements are spaced from each other by a predetermined distance, the signals therefrom will have aphase difference that is a function of the angle of incidence of the received wave front upon the antenna elements. Separate reciprocal phase Shifters are provided for at least a portion of the antenna elements for shifting 7 nited States Patent O the phase of any signals passing therethrough, Phase comparator means are interconnected with at least one of said elements and the output of one of said phase Shifters so as to compare the phases of the two signals and provide a control signal that is proportional 'to the difference between the two phases. This control signal is fed to each of the phase Shifters and will thereby be effective to control the amount of phase shifting occurring in each of the phase Shifters. More particularly, the control signal may be effective to adjust the phase shifter to maintain the phase difference between the signals reduced to zero. With the phase Shifters thus adjusted, the antenna pattern will be maintained normal to the wave front incident thereon. Thus, employing a suitable array of elements, the pattern of the array may be focused into as narrow a beam as desired and by providing separate phase shifters for the additional elements together with proportional control signals therefor, the antenna pattern will always be centered upon the direction from which the received signal is coming. If the antenna elements and the phase Shifters therefor are all reciprocal, transmitting means may be provided for feeding electromagnetic energy through the phase Shifters to the various elements so as to lcause an electromagnetic signal to 4be radiated. Since the phase Shifters will be effective to maintain the antenna pattern aligned with the received signal, the signals radiated from the individual elements will have the proper phase relations to combine into a beam having a narrow beam width which is centered on the same line from which the received energies are traveling.

It may thus be seen that the phase Shifters and control means therefor will be effective to form a closed loop circuit which will automatically adjust the phase of the signals for each of the antenna elements to insure the receiving and transmitting antenna patterns being automatically centered on the axis of any signals incident thereon. As a result, the antenna may have a very narrow pattern whereby the energy in a signal may be concentrated in a beam aimed directly at a second station.

Thus efficient communications will be insured between the two stations.

These and other features and advantages of the present invention will become more readily apparent from the following detailed description of the invention particularly when taken in connection with the accompanying drawing wherein like numerals designate like parts and wherein:

The drawing is a block diagram of an antenna array and control means therefor which embodies the present invention.

Referring to the drawing in more detail, the present invention is embodied in an antenna array 20 and the control system 22 therefor. The antenna array 20 includes a plurality of elements that may be arranged into any desired conguration of either two or three dimensions for use in any portion of the frequency spectrum such as the so-called microwave region. The number and configuration of the elements may be chosen to provide an antenna array 20 having a sensitivity pattern with the desired beam characteristics. The antenna elements may be any of the well known variety such as dipoles, resonant apertures, etc.

For purposes of illustration in the present ins-tance, the

`array Z0 is shown as a linear array 20 wherein elements are arranged in a stra-ight line so as to form a first group of elements 1, 2, 3, N and a second group of elements, 1', 2', 3', N. T-hese groups and the elements therein are shown as being symmetrically disposed about a center line -or axis 24 of the array 20 that extends between elements 1 and 1. It should be understood that the elements may be symmetrical about a center line located anywhere within the array or may even be asymmetrical 3 if desired. In addition, the spacing between the elements may be uniform or irregular if desired.

If electromagnetic energy is radiated from a source such as a remotely located station, the radiations will form a Wave front consisting of planes where the phase of the radiations are uniform. These planes of equal phase are illustrated in the drawings as lines 26 of equal phase that are substantially normal to the axis 28 of propagation.

When the antenna elements are arranged in a straight line, in the event the axis 28 of a Wave front is oblique to the axis 24 of the array 20, the wave Ifront will strike the element N nearest to the source first. It will then successively strike the succeeding elements N-l, 3, 2, 1, 1', 2', 3', N after predetermined time delays. The duration of the time delays will be a function of the spacing between the antenna elements and if each of the spacings or ydistances between the adjacent elements are all equa'l, the time delays will all be equal. In addition, as may be seen from the drawing, the amount of time delay with which the phase fronts 26 strike t-he succeeding elements will also be dependent upon the angle formed between the axis 24 of the antenna array 20 and the axis 28 of propagation.

It may thus be seen that when a wave front 26 of electromagnet-ic radiation in the microwave region is incident upon each of the elements, each of the elements will provide a microwave signal that is characteristic of the electromagnetic radiations and will have a phase relation that is a function of the angle of incidence of the radiations.

Each of the elements 1, 2, 3, N and 1', 2', 3', N may be connected to a transmission line 31, 32, 33, 3N or 31', 32', 33', 3N' respectively. The transmission lines may be so called wave guide, co-axial line, strip line or any other form of transmission means suitable for use in the frequency range being employed. One of these elements 1' comprises a rre-ference element, While the rest of the elements are secondary elements. The transmission l-ines 31 through 3N and 32' through 3N from each of the secondary elements 1 through N and 2' through N respectively may lead to an input of a variable phase shifter 41, 42, 43, 4N and 42', 43, 4N'. These phase shifters which are preferably all substantially identical to each other may be any of the well known varieties such as those employing a mechanically movable reactance member, a voltage responsive reactance member or a current responsive reactance member. For example, each of the phase Shifters may have a ferrite element therein which may be energized by means of a current flowing through a solenoid wound around the ferrite element. Such a ferrite element may be a reciprocal reactance that will be effective to produce a phase `shift that will be identical for energy owing therethrough in either direction and will have a magnitude determined by the amount of current flowing through the solenoid. It may thus be seen that by employing a separate control conductor 51, 52, 53, 5N and 51', 52', 53', 5N' for each of the phase shifters 41, 42, 43, 4N and 41', 42', 43', 4N' and providing a suitable control signal thereto, each of the phase Shifters will be effective to cause any microwave signals passing therethrough to have the phases thereof shifted. Each of the phase shifters 41, 42, 43, 4N and 42', 43', 4N' will cause the signals therein to be separately shifted by amounts that will be a function of the control signals applied thereto. Thus, by supplying separate control signals on each of the conductors 51, 52, S3, 5N and 52', 53', 5N' the amounts of phase shift gbl, 752, gba, N and 2', das', 45N respectively in each phase shifter may differ from the amount of shift in the other phase Shifters.

It may thus be seen that each of the phase Shifters 41, 42, 43, 4N and 42', 43', 4N' will shift the 4 microwave signals from the associated antenna elements by angles that are determined by the control signals on the conductors 51, 52, 53, 5N or 52', 53', 5N'. A suitable transmission line 71, 72, 73, 7N and 72', 73', 7N is connected to the outputs from each of the phase Shifters whereby the signals from the antenna' elements will be present-in t-hetransmission lines 71, 72, 73, 7N and 72', 73", 7N'.

The transmission linesy 71, 72,73, 7N from the phase shifters 41,v 42, 43, 4Nyfrespectively may be joined to a common transmission line that is connected to the transmission line 81 by a suitable isolating or switching means 82. This isolating means 82 may be effective to isolate the element 1 from the elements 2, 3, N or to effectively interconnect all of the antenna elements together to form them into a first group. This isolator may be a` suitable mechanical switch mechanism or any other suitable means such as a conventional gas-filled tube operated as a switch for interconnecting the phase Shifters together in the manner to be explained subsequently. Thus, all of the elements 1, 2, 3, N and the phase Shifters 41, 42, 43, 4N therefor may form a first group whereby the signals therefrom ma all be present on the transmission line 81.

The transmission l-ines 72', 73', 7N' from the phase shifters 42', 43', 4N' may be joined to a common transmission line 83 that leads to a second isolating or switching means 84. This means 84 may be similar to the means 81 so as to effectively control the interconnection of the transmission lines 31' and 83. Although the operation of the means 84 will be explained subsequently, it may be seen that the eleme-nts 1', 2', 3', N' and the phase shifters 42', 43', 4N' therefor may form a second group whereby the signals therefrom may be combined with each other and present on the transmission line 85.

The first transmission line 81 may lead to the first input of a mixer 86 of any suitable variety while the transmission line 85 may lead to the first input of a second mixer 87 also of `any suitable variety. In the event it is desired to transmit signals from the antenna array 20, suitable diplexers -or duplexers 124 and 126 may be provided in the transmission lines 81 and 85 respectively for interconnecting the transmission lines 81 and 8S with a suitable source of microwave energy such as a transmitter 122. The operation of 4the transmitter 122 and diplexers or duplexers 124 and 126 will subsequently be explained in more detail. Each of the mixers 86 and 87 may also include second inputs 88 and 89 for receiving a second signal. These inputs 88 and 89 are connected to a common local oscillator 90 having a frequency that differs from the frequency of the radiations to be received by a predetermined amount. It may thus be seen that the 'signals in the transmission lines 81 and 85 will beat with the local oscillator signal to produce a vbeat frequency signal or an IF signal having a frequency equal to the intermediate frequency. The IF signals will be present in the outputs of the mixers 86 and 87. A separate' transmission line 91 and 92 may be Aconnected to the outputs from the mixers 86 and 87 so as to lead to the inputs of intermediate frequency amplifiers 93 and 94. These amplifiers 93 and 94 may have sufficiently narrow bandwidths to amplify only the IF signals to a more useful level.

A phase comparator 95 may be provided for comparing the phases -of the signals in the `outputs of the IF amplifiers `93and 94 and providing a signal indicative of the difference 'between the phase angle thereof, The phase comparator includes two separate inputs 96 land l97. The first input96 is connected to the output from the first intermediate lfrequency amplifier 93 by means of a transmission line 98 ywhile the second input 97 is connected to the `output from 'the second intermediate frequency amplifier 94 by means offa transmission line 99. The phase comparator.l 95 may ybe. effective to compare the two amplified intermediate frequency signals andproduce a dif- -tional phase shifts gbl, p2, cpg,

ference signal that is indicative of the difference in the phase angles between the signals from the antenna elements land 1 or the two signals from the gr-oups depending upon the isolator means 82 and 84. Normally the energy that is incident upon the antenna elements will be in the form of relatively short duration pulses with intervals therebetween when no energy is received. As a result the inputs 96 and 97 will receive corresponding pulses for comparison. Normal-lyif there is a phase differential between the two signals, the difference signal `will have some measurable amplitude. However, if there is no phase difference between the twosignals normally the output signalwill have zero amplitude. Thus, in s-uch a comparator `a pair of signals in phase with each other and the n0 signal condition occurring between pulses will produce identica-l outputs at the output of the phase comparator 95.

To overcome the foregoing difiiculty, the output of the phase comparator 95 may be connected to the input of an 4integrator 100 so that the output or difference sign-al will 'be supplied thereto. The integrator 100 will be effective to integrate pulses forming the difference signal and thereby provide a. control signal. The integrator 100 may be of any well known variety. The time constant yof the integrator 100 may be chosen so as to hold the pattern in position for any desired period. Thus, although the difference signal may fall to zero between pulses, the control signal from the integrator will remain substantially constant for extended periods and will only vary in amplitude at a rate corresponding to the rate at which the bearings between sending and receiving stations vary. A pair of conductors 102 and 103 may be connected Iwith the output of the integrator 100 so as to feed the co-ntrol signal to a pair of control amplifiers 104 and 105.

The first control amplifier 104 includes a single input but separate outputs 111, 112, 113, 11N for each of the phase shifters 41, 42, 43, 4N respectively in the first group. The conductors 51, 52, 53, SN are connected to these outputs so that a separate control signal will be applied to each of the phase shifters. Each of these separate control signals may be in some predetermined relation to' the control signal from the integrator 100 and will thereby be effective to provide corresponding proporqbN of microwave signals passing through the phase Shifters 41, 42, 43 .4N.

Each of the control amplifiers 104 and 105 may be vconstructed in a conventional manner and may be provided with a plurality of output terminals or taps for providing the diffe-rent -outputs such as the outputs 111,

112 and 113, For example, the outputs 111, 112 and 113 Vmaybe different voltages from the amplifier 104, the

values of these voltages `depending upon the signal from the integrator 100. Sin-ce the outputs 111, 112 and 113 constitute different voltages, they are respectively instrumental in causing the phase shifters 41, 42 and 43 to produce different phase shifts.

The second control amplifier 105 is similar to the first amplifier 104 in that it also includes separate output 112',

113', 11N' for each of the phase Shifters 42', 43, 4N i-n the second group. These outputs are interconnected with the conductors 52, 53', `5N' and also provide signals proportional to the output or control Asignal from the integrator 100. Thus, each of the phase -shifters 42', 43', 4N will also provide proportional phase shifts 412', Q53', qbNf for the microwave signals passing therethrough.

A receiver 120 may be provided that may be interconnected with an output of the phase comparator 95 or with the outputs of the IF' amplifiers 93 and 94. The receiver 120 may be tuned to the intermediate frequency and includes suitable utilization means such as a remote control for actuating the transmitter 122, s

In order toemploy the present antenna arrav and the control means 22 therefor, Iall of the various components are placed in an operative condition. The antenna array 20 is then physically oriented so that a remote staltion with which it -is desired to communicate has a bearing that is somewhere within the scan angle of the array 20. In the event 'the remote station is radiating microwave energy tow-ard the antenna array 20, the wave front wi-ll strike the reference element 1 and the element 1 and will result in microwave s-ignals being present in the transmission lines 31 and 31. If the isolating means 82 and 84 are effective to prevent the signals in the lines and 83 entering lines 81 and 85, only the signals from the elements 1 and 1' will be present on the lines 81 and 85. Since only the elements 1 and 1 are effective when operating in this mode, the array 20 wi-ll have a very wide pattern. As a result the presence Iof a signal from a source located anywhere within the scan angle of the array will be effective to actuate` the control means 22.

It will be seen from the discussion in the previous paragraph that the isolating means 82 is effective in one state of Ioperation to prevent signals from the line 80 from passing through the isolating means; In this state of operation of the isolating means 82, only the signals from the phase shifter 41 are present on the line 81 to control the introduction of signals from the control amplifier 104 to the phase Shifters 42 and 43 to obtain phase shifts by 4the phase shifters. The isolating means 83 operates in a similar manner to prevent the signals from the phase Shifters 42' and 43 from passing through the isolating means.

Energy incident upon the element 1 will travel along the transmission line 31, through the phase shifter 41 and into the transmission line 71. The -signals will then pass through the isolator means 82 and onto the transmission line 81. The energy incident upon the element 1 will travel along transmission line 31 through t-he isolator means 84 and into the line 85. The signals in the lines 81 and 85 will thus have signals with a phase difference that will be a function of the angle of incidence 0 and the phase shift angle qsl in the phase shifter 41. These two signals may then travel along the lines 81 and 85 through the diplexers or duplexers 124 and 126, if present, and into the mixers 86 and 87. Here the signals will beat with the total ocsillator to produce IF signals in the transmission lines 91 and 92. These signals will then be fed to the IF amplifiers 93 and 94 where they will be amplified to a more useful level. The amplified IF signals may then be fed to the phase comparator 95. The phase comparator 95 will compare the phase of the two signals or transmission lines 98 and 99 and provide a difference sign-al. The amplitude of the signal will be a function of the difference between the phases of the two signals and the time duration thereof will be similar to the time duration of energy incident upon the antenna elements 1 and 1. Since the received signals will normally be relatively short duration pulses, the difference signal will also be a short duration pluse. During the intervals between the pulses the difference signal will be zero.

The difference signal, in its pulse form, is then fed to the integrator 100 which will provide a control signal indicative of the difference signal. The integrator 100 preferably h-as a relatively long time constant. As a result, the signal in the output of the integrator will be maintained at a substantially constant level for extended periods. If desired, the time constant of the integrator may be much longer than the intervals between the succeeding pulses being received by the array 20. This will result -in a control signal that will remain substantially uni- -form between pulses although it may vary very slowly over extended periods. Although the bearing between two stations will remain relatively constant, the integrator must have a sufiicient response to vary at a r-ate corresponding to the rate at which the bearings change.

resultant control signal from the integrator Y100 will be proportional to the difference between the signals from the elements 1 and 1'. As a result, the control signal supplied to the phase shifter 41 will be effective to cause the phase shift gbl in the shifter 41 to be equal and opposite to the phase difference between the original signals. This in turn will cause the signals in transmisison lines 81 and 85 to be -in phase with each other.V

As -a result of the phase shift, the effective pattern of the antenna elements 1 and 1 will be centered upon a line extending toward the source. Although the relative broad pattern formed 'by only the two elements 1 and 1' is best suited for the initial acquisition of a signal, once the array and the control means 22 therefor have located a source and has aimed the pattern thereonit may be de- -sirable to employ a narrower, higher gain pattern for further reception and/ or tracking of the source. Accordingly, the isolation means 82 and 84 may be actuated by signals on the conductors 130 and 132 leading from the amplifiers 104 and 105. This will cause the isolator means 82 and 84 to interconnect the lines 80 and 81 together and 8,3 and together. Thus, the signals from e-lements 2, 3, N and 2', 3', N' will be fed into the transmission lines 81 and 85 where they will combine with the signals from elements 1 and 1'. When operating in this mode, the array 20 will have a much narrower pattern that will insure a stronger received signal with less relative noise. Since the phase comparator 9-5 will provide a difference Signal that now -indicates the phase difference between the signals from the two groups of elements, the

amplifiers 104 and 105 Iwill be effective to maintain even the narrow beam centered on the axis 28.

It may thus be seen that the antenna array 20 may have a very broad pattern while operating in an acquisition mode for locating a signal source. However, once a signal source has been located and the antenna pattern has been aimed thereat, the isolator means 82 and 84 will cause all elements to become operative whereby the antenna pattern will become narrow so as to more accurately track the signal source.

As will be seen from the discussion above, the isolating means 82 operates in one state to prevent the signals on the line 82 from passing through the isolating means. This means that the phase comparator is responsive only to the signals from the phase shifter 41 and not to the signals from the associated phase Shifters such as the phase Shifters 42 and 43. Accordingly, the output 130 from the control amplifier 104 is dependent only upon the signal from the phase shifter 41 and not from the associated phase Shifters such as the phase Shifters 42 and 43.

The signal produced by the phase comparator 104 is instrumental in controlling the phase shift provided by the phase Shifters 41, 42 and 43 so that the output signals from these phase Shifters approximate the same phases even though the antennas 31, 32 and 33 may be receiving signals of different phases. Furthermore, the signals from the phase shifter 41 may have approximately the same phase as the signals from the antenna 1'.

Since the phase shifter 42 and the antenna 1' provide signals of approximately the same phase, the phase comparator 95 provides a signal of relatively low amplitude. This causes the control amplifier 104 to provide outputs 111, 112, 113 and 130 of relatively low amplitude. As -will be appreciated, the output is similar to the outputs 111, 112 and 113 in that it constitutes a voltage which may be obtained from a tap, just as the outputs 111, 112 and 113 constitute voltages which may be obtained from taps.

When the output 130 falls below a particular value in amplitude, it causes the isolating means 82 to become operative in a second state. For example, the isolating means may be a conventional amplifier which is biased to a state of non-conductivity and which is triggered to a state of conductivity when the output 130 falls below 8 the particular level in amplitude. By way of further illustration, the conventional amplifier constituting the isolating means 82 may have a gas-filled tube as the switching element so that the amplifier remains in its second state of operation once the gas-'filled tube 4has been triggered to the conductive state.

In itssecond state of operationfthe isolating means 82 passes the signals on the line 801 Since the signals from the phase Shifters 42 and 43 will generally have a greater error'than the signals from the phase shifter 41', signals of increased error become introduced to the phase comparator 95 through the duplexer' 124. At the same time, the isolating means 84 also becomes triggered to its second state since the isolating means 84 is constructed r in a manner similar to the isolating'means 82.This causes signals of increased error to pass through the duplexer 126 to the phase comparator 95 from' the phase Shifters 42 and 43'. i

Since the phase comparator 95 receives signals of increased error, it produces an error signal of increased amplitude. This causes signals of increased amplitude to be produced by the amplifiers 104 and 105 so that further phase shifts are provided in the phase Shifters 41, 42 and 43 and in the phase Shifters 42 and 43'. In this way, the isolating means 82 and 84 are effective in one State to obtain a coarse control over the operation of the phase Shifters and are effective in the second state to obtain a fine control over the operation of the phase Shifters.

In the event it is desired to maintain two way communication between a remote station and the present installation, a source of electromagnetic energy of suitable frequency may be provided. In the present instance, this source comprises a transmitter 122 capable of generating energy of suitable frequency and modulating the energy in the required manner. Although the transmitter 122 may be interconnected with the antenna elements 1, 2, 3, N and 1', 2', 3', N by any suitable means, in the present instance isolating means are provided in the transmission lines 81 and 85. The isolating means may comprise diplexer or duplexer means 124 and 126. Each of these means which include an input and 142 connected to the transmitter 122 by suitable transmission lines 144 and 146 may be of any suitable variety for effectively isolating the mixers 86 and 87, the IF amplifiers 93 and 94, the phase comparator 95 and receiver from the large amounts of power from the transmitter 122. For example, the means 124 and 126 may be a mechanical or electronic switching vmechanism for alternately connecting the isolator means 82 and '84 to the transmitter 122 or for connecting the isolator means 82 and 84 to the mixers 86 and 87 may be employed. Alternatively, this means 124 and 126 may be a suitable directive coupling, filter means or other suitable means for permitting received energy to travel fromwthe isolator means 82 and 84 directly throughthe transmission lines 81 and 85 to the mixers Awhile permitting energy in the transmission lines 144 and 146 to be launched into the transmission lines 81 and 85 soas topropagate only the direction of the isolator means 82 and 84.

It may thus be seen that .when transmitting theenergy from the transmitter 122 will propagate along the transmission lines 81 and 85 to the, isolator means 82 and 84. The energy in the isolator means 82.will lthen enter line 71 and preferably line 80 whereby-the energy will pass through the phase Shifters 41, 42, 43, 4N to the antenna elements 1, 2, 3, N. The energyin the isolator means 84 lwill simultaneously enter the transmission line 31' and preferably also transmission line 83' and phase Shifters 42', 43'-, 4N' whereby the energy will excite the antenna elements 1', 2', 3', N'.'AS a result, the energy from the transmitter' will be radiated from the elementsin the form of a'beam having apattern and direction that will be determined by the phase'relations of the energies from the elements.

` If .a signal hasbeen received by the array l20 and it is still within the time delay period ofthe integrator 100, the amplifiers 104and l'10S-.will be supplying control signals to all of the phase Shifters. Since the phase Shifters are-all reciprocal, the `transmitted energies passing therethrough will be shifted by the. same number ofdegrees as the receivedenergies. As a result, the-transmitting energiesarriving at the antennaelements will have the same phase relationsas the energy `that is beingreceived. This in turn will cause the radiated energies to be formed into a beam that will be directed along the axis 28.

In order to obtain increase in the efficiency of transmission, it isdesirable for the energy to be concentrated in as narrow a beamas possible. Thus, even though only elements 1 and 1 are beingA used to receive, the isolating means 82l and 84 are preferably effective to cause all of the antenna elements in the array to be employed for transmitting. By='employing all of the elements 1, 2, 3, N and 1', 2' 3', N, a very narrow'beam may be radiated. Moreover,'since the phase shifters 41, 42, 43, t 4Nand 42', 43,f. 4N will all `be controlled in response to a received signal, the radiated beam will automatically bemaintained properlycentered on the axis of the received signal.l f v The isolator means 82 and 84 may be effective to prevent the received energy intransmission lines 80 and 83 entering the transmission lines 81 and 85 while at the same time permit the transmitted energy in transmission lines 81 and 85 to be coupled into fthe lines 80 and 83. Thus the array 20 may receive with' a very widepattern while at the 'same time it may transmit with a very narrow pattern that will be accurately aimed at the source from which energy is being received.

It may thus bel seen that an antenna array and the control means therefor have been provided that will be effective to keep-the pattern thereof accurately centered on the axis of any signals received thereby so that the antenna will insure a maximum sensitivity when operating'in both the transmitting and receiving modes. Although only a single embodiment of the present invention -has` been disclosed,` it will be readily'apparentto those skilled in the art that numerous changes and modifications may be made without departing from the spirit of the invention. For example, it may be desirable for the center line 24 of the array 20 to extend through the reference element 1 with the spacings between the elements 1 and 1' and the elements 1 and 2 being equal. Witha center line'extending through the reference element 1 and the elements being "disposed symmetrically about that line,l the phase lshifts in` the shifters 41 `and 42 and the remaining symmetrically disposed pairs will-be equal but of opposite sense. In'addition, the same techniques may be employed to extend the'invention to include'a two dimensional array. Accordingly, the foregoing description and drawing are for `illustrative purposes only and are notl intended to ing energy from an electromagnetic source comprising the combination of a plurality of antenna elements providing a narrow beam width sensitivity pattern and arranged to receive energy from the electromagnetic source, useparate variable phase shifting means for a portion of said, antenna elements; control means for generating a separate control signal for each phase shifter, each of said control signals being an analog signal that is continuously variable throughout a predetermined range, eachV of said phase shifting means being operatively interconnected with a separate antenna element and with said control means, said phase shifting means being responsive to said controlsignals and effective 10 to continuously vary the phase of the signal passing therethrough,

said control means being responsive to the signal from a pair of the plurality of said antennal elements to provide control signals for continuously varying the amounts of phase shifts in said phase shifters to cen- -ter the narrow beam width sensitivity pattern provided by the antenna elements in the direction of the electromagnetic source.

2. Electromagnetic energy antenna means comprising the combination of a reference antenna element and a plurality of secondary antenna elements spaced from each other and said reference element, each of said elements being positioned to receive energy from anelectromagnetic source and produce `a microwave signal in response thereto,

a variable phase shifting means operatively interconnected with each of said secondary elements, each of said phase shifting means including a control input and means for varying the phase ofsaid microwave signals passing through in proportion to the amplitude of a control signal applied to ysaid input, Y

phase comparing means operatively interconnected with at least one of said phase shifting means and being responsive to the signal from said reference element and the signal from the secondary elements corresponding to the last mentioned phase shifting means to provide a control 1signal that is a function of the difference between the phases of the microwave signals on said elements,

control means operatively interconnected with said phase comparison means to provide separate control signals for each phase shifting means that are functions of said output signal, ysaid control means being interconnected with each of said phase shifting means to supply said control signals to vary the amounts of phase shift in each of said shifting means to maintain predetermined phase differences between the microwave ysignals from said phase shifting means.

3. Electromagnetic energy antenna means comprising the combination of Y a first group of antenna elements disposed in a substantially straight line,

separate phase Shifters for at least a portion of the elements in said second group,

a second group of antenna elements disposed in said straight line symmetrically with respect to said first to form a linear array,

a separate phase shifter for at least a portion of the elements in said second group,

first transmission line means operatively interconnected with the phase Shifters and said elements in said first group,

a second transmission line means operatively interconnected with the phase Shifters and elements in said second group,

switch means in said transmission line means operative between a first condition wherein all of the elements in said groups are operatively interconnected with said transmission line and a second condition wherein only one element in each group is operatively interconnected with said transmission means, and

phase comparator means interconnected with said first and second transmission line means for sensing the phase relations of the signals from said groups when said switch means is in said second operative condition, operatively interconnected with said phase shifters for varying the phase shifts therein until the difference between the signals in said irst and second transmission line means is zero.

4. Electromagnetic energy antenna means comprising the combination of a plurality of antenna elements, said elements being disposed in a substantially straight line to form a linear array which includes a first group of said antenna elements and a second group of said antenna elements symmetrically disposed with respect to said first group, each of said elements being positioned to receive electromagnetic energy and to provide a microwave signal in response thereto,

first transmission line means interconnected with the elements in said first group, said transmission means including a separate variable phase shifter for at least a portion of the elements in said first group to thereby variably shift the relative phases of each of said microwave signals in said first group,

a second transmission line means interconnected with the elements in said second group, said second transmission line means including a separate variable phase shifter for at least a portion of the elements in said second group to thereby variably shift the 12 between the electromagnetic energy incident on said pair of elements to provide an analog signal thatis continuously variable throughoutv a predetermined range, and

- means operatively interconnecting said control means the combination of a reference antenna element for receiving a beam yof electromagnetic energy and providing microwave signals in response thereto,

a plurality secondary antenna elements disposed ad,- jacent said reference ele-ment to receivesaid electromagnetic energy to provide separate microwave signals in response thereto,

relative phases of each of said microwave signals g() a separate reciprocal transmission line interconnected in said second group, within each of the transmission lines for said secfirst switch means in said first transmission line means ondary antenna elements, said phase shifting means operative between a first condition wherein all of the being reciprocal and effective to vary the phases of elements in said first group are connected to said the microwave Signals traveling in the transmission first transmission line means and a second condition lines for said secondary elements wherein only one of the elements in said first group a source of electromagnetic energy, is operatively connected to said first transmission phase comparator means, line means, switch means operable between a first condition wheresecond switch means in said second transmission line in said reference element and one of said secondary means operative between a first condition wherein elements are connected to said phase comparator, all of the elements in said second group are conand a second condition wherein all said phase shiftnected to said second transmission line means and ers are connected to said source for transferring ena second condition wherein only one of the elements ergy from said source to said antenna elements for in said second group is operatively connected to said radiating energy therefrom as a beam, second transmission line means, and said phase comparator being effective when said switch phase comparator means having a first input interconis in said first condition to provide a control signal nected with said first transmission line means, and a proportional to the phase relation between the sigsecond input interconnected with said second transnal from said reference element and the signal from mission line means, said phase comparator means besaid phase shifter, and ing effective when said switch means are in said sec- 4.0 control means operatively interconnected with said ond condition to provide a separate control signal for phase comparator .and responsive to said control sigeach of said phase Shifters, said control signals being nal and interconnected with said phaseshifters for effective to provide a phase shift in each of said shifting the phase of the energy fed to said elements phase shifters that will cause the signals therefrom whereby said elements will be excited to radiate a to all be in phase with each other. beam of the energy having an axis coincident` with 5. Electromagnetic energy antenna means comprising the combination of at least two reciprocal antenna elements, a source of electromagnetic energy,

a plurality of transmission line means interconnecting y reciprocal phase shifting means in at least a portion of said transmission line means for varying the phases of thc energies passing therethrough,

control means operatively interconected with said pair of elements and responsive to the difference in phase the direction of said first beam. 8. Electromagnetic energy antenna means comprising the combination of a reference antenna element and a plurality of secondary antenna elements spaced from each other and said electromagnetic source with each of said eledo said reference element, each of said elements being ments for supplying energy to said elements for radireciprocal and positioned to receive a beam of enerating a beam of electromagnetic energy therefrom, gy from a remote electromagnetic source and to proand duce microwave signals in response thereto and to phase shifting means in at least one of said transmiss, receive microwave signals from a transmitter and sion means for varying the phases of the electro- 0') r'adiate a beam of electromagnetic energy toward magnetic energy passing therethrough, said remote source, control means responsive to the phase of energy incia variable phase shifting means operatively intercondent upon said antenna elements to vary the amount nected lwith each of said secondary elements, each of phase shift in said phase shifting means to mainof said phase shifting means rbeing reciprocal and tain said radiated beam aligned with the source of effective to separately vary the phases of said sigsaid incident energy. nals traveling to and from said secondary elements, 6. Electromagnetic energy antenna means for radiating a transmitter for generating microwave signals, a return beam of energy back along the path of energy phase comparator means for being operatively interincident upon said means, said antenna means comprising 67 connected with one of said phase Shifting means and the combination of o said reference element, said phase comparator means aplurality of antenna elements, being responsive to the pair of microwave signals a SOUTC@ 0f electromagnetic energy, therefrom to provide a control signal that is a funca plurality of transmission line means interconnecting tion of the difference between the -phases of said pair said source with each of said antenna elements, 70 of signals,

switch means having a first operative condition effective to connect all of said phase shifters to said transmitter and a second operative condition effective to connect said reference element and one of said secondary elements to said phase comparator,

said phase comparator during said second condition being effective to supply said control signal to said phase shifter means to vary the amount of phase shifts therein so that said transmitter will excite said elements to radiate a beam of energy coincident with said first beam.

9. Electromagnetic energy antenna means for radiating a beam of energy back along the path of energy incident upon said means, said antenna means comprising thecombination of a plurality of antenna elements arranged to form an array having a reference element and a plurality of secondary elements,

a source of electromagnetic energy,

transmission means interconnecting said source with each of said antenna elements, separate phase shifting means in each of the transmission means connected to said secondary elements, said phase shifting means being effective to change the phase of the energy passing therethrough, and

means responsive to the difference in phase between the electromagnetic energy incident on said reference element and at least one of said secondary elements, said last mentioned means being operatively interconnected with each of said phase shifting means for varying the amount of phase shifting therein so that energy from said source radiated from said antenna elements will form a wave front directed along said path.

10. Electromagnetic energy antenna means for receiving a series of pulses of electromagnetic energy and radiating a beam of energy back along the path of said pulses, said antenna means comprising the combination of a plurality of antenna elements arranged to form an yarray having a reference element and a plurality of secondary elements, each of said elements being effective to receive a series of signals and to provide a series of microwave signals,

a source of electromagnetic energy,

transmission means interconnecting said source with each of said antenna elements,

a separate p'hase shifting means in each of the transmission means connected to said secondary elements, said phase shifting means being responsive to a control signal and effective to change the phase of the energy passing therethrough as a function of said control signal,

phase comparing means operatively interconnected with said reference element and the output of one of said phase Shifters, said phase comparing means being responsive to the difference in phase of the series of microwave signals from said reference element and one of said phase shifting means so as to produce a control signal,

integrating means operatively interconnected with said phase comparing means and responsive to said control signal, said integrating means having time constant that is long compared to the time between the signals said series,

control means operatively interconnected with the output of said integrating means to provide a separate control signal for each phase shifter that are functions of said first control signal, said control means being operatively interconnected with each of said phase shifting means for feeding the control signals thereto for varying the Iamount of phase shifting therein so that a beam of the energy from said source will be radiated from said elements.

11. Electromagnetic energy antenna means for radiating a beam of energy lback along the p-ath of energy incident upon said means, said antenna means comprising the combination of a first group of antenna elements disposed in a straight line,

a second group of antenna elements disposed in said straight line symmetrically with respect to said first group to form alinear array,

separate phase shifters for at least a portion of the ele` ments in said first group,

separate phase Shifters for at least a portion of the elements in said second group,

each -of said phase shifting means being reciprocal and effective to change the phase of energy passing there through in response to a control signal,

a source of electromagnetic energy,

first transmission line means,

switch means in said transmission line means having a first operative condition effective to interconnect said source with each of said antenna elements in said first group and a second operative condition effective to interconnect said source with only one of the elements in said second group,

second transmission line means,

second switch means in said second transmission line means having a first operative condition interconnecting said source with each of the antenna elements in said second group and a second operative condition interconnecting said source with only one of the elements in said second group,

phase comparator means operatively interconnected with each of said transmission line means and effective when said switch means are in said second condition to provide a difference signal that is a function of the phase difference between the signals from said groups,

control means operatively interconnected with said phase comparator and responsive to said difference signal to provide a separate control signal for each of said phase Shifters, said control means being operatively interconnected with said phase Shifters for feeding said control signals to said phase shifter and effective to vary the phases of energie-s fed from said source to said elements when said switch means are in said first condition so that said energy radiated from said elements will form a wave front symmetrically disposed about said path.

References Cited UNITED STATES PATENTS 2,173,858 9/1939 IPierce et al 343-854 X 3,036,210 5/1962 Lehan et al. 343-854 X 3,056,961 10/1962 Mitchell 343-854 2,975,275 3/1961 Adams 343-117 2,042,831 6/ 1936 Crosby. 3,138,800 6/1964 Speller 343--117 OTHER REFERENCES Journal of the Patent Office Society, vol. 31, No. 8, pp. 634-635, August 1949.

Sommer, I.R.E. Transactions on Aeronautical and Navigational Electronics, vol. ANB-3, No. 2, June 1956, pp. 67-70.

'RICHARD A. FARLEY, Primary Examiner.

R. E. BERGER, Assistant Examiner. 

2. ELECTROMAGNETIC ENERGY ANTENNA MEANS COMPRISING THE COMBINATION OF A REFERENCE ANTENNA ELEMENT AND A PLURALITY OF SECONDARY ANTENNA ELEMENTS SPACED FROM EACH OTHER AND SAID REFERENCE ELEMENT, EACH OF SAID ELEMENTS BEING POSITIONED TO RECEIVE ENERGY FROM THE ELECTROMAGNETIC SOURCE AND PRODUCE A MICROWAVE SIGNAL IN RESPONSE THERETO, A VARIABLE PHASE SHIFTING MEANS OPERATIVELY INTERCONNECTED WITH EACH OF SAID SECONDARY ELEMENTS, EACH OF SAID PHASE SHIFTING MEANS INCLUDING A CONTROL INPUT AND MEANS FOR VARYING THE PHASE OF SAID MICROWAVE SIGNALS PASSING THROUGH IN PROPORTION TO THE AMPLITUDE OF A CONTROL SIGNAL APPLIED TO SAID INPUT, PHASE COMPARING MEANS OPERATIVELY INTERCONNECTED WITH AT LEAST ONE OF SAID PHASE SHIFTING MEANS AND BEING RESPONSIVE TO THE SIGNAL FROM SAID REFERENCE ELEMENT AND THE SIGNAL FROM THE SECONDARY ELEMENTS CORRESPONDING TO THE LAST MENTIONED PHASE SHIFTING MEANS TO PROVIDE A CONTROL SIGNAL THAT IS A FUNCTION OF THE DIFFERENCE BETWEEN THE PHASES OF THE MICROWAVE SIGNALS ON SAID ELEMENTS. 